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  1. #41
    Lee L's Avatar
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    Quote Originally Posted by Poisson Du Jour View Post
    ... gel filters are lousy for any photography...
    Before digital, gel filters were the de facto standard and first choice for 4x5 and larger format studio photography. In large format they are often used in a filter holder on the back of the lens, protected inside the camera bellows. It was common to stack up to three filters for color correction on E6 film. Gels have excellent optical qualities, even compared to the best glass filters.

    I would agree that gels are not so great in front of the lens for field work, but only because of their more fragile nature and difficulty in cleaning them, not because of optical shortcomings.

    Lee

  2. #42

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    Quote Originally Posted by bowzart View Post

    Maybe you are thinking that a pinhole image should compete with a lens on the lens' terms. It can't, and ought not be expected to. If it did, why bother? The parameters are different. Lenses and pinholes are NOT the same thing, and what they do is different. You can have a sharp image from a pinhole, but it doesn't look like a sharp image made with a lens.
    No, I certainly do not expect it to compete with a lens. If I wanted an image like that, I would use a regular camera and lens. The distance is 3 inches.

    It may indeed be sharp. Likely I will just sacrifice a roll of film and see how it works. As expected it is really dark therefore I may not be seeing the image that well.
    Bachelor of Fine Arts and Bachelor of Arts: Journalism - University of Arkansas 2014

    Canon A-1, Canon AE-1, Canon Canonet GIII 17, Argus 21, Rolleicord Va, Mamiya RB67, Voigtländer Bessa

    http://darkroom317.deviantart.com/

  3. #43
    Pavel+'s Avatar
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    Details ....

    I'm a little late to this discusion but wanted to chime in with my observation about what Ralph has stated and illustrated well with his diagram - that pinhole size affects angle of view.

    As far as it has been illustrated the diagram would serve to support the assertion that size does in fact affect angle of view. However .... it does not.

    The detail omitted is the film size. The diagram, if it is to be made more complete would show the film. Draw a same size, lets say one inch line under each of the diagrams. This would represent the boundary of your film size and then we will see that in the first expample if the film is far enough back a too small hole would cause dramatic vignetting where the light does not reach directly but only through bouncing around. If the second size is taken as correct and being larger enables light traveling in a straight line to reach the corners then a larger hole will only have more of the light hit areas inside the camera that are the sides, not on the film but if you measure the angle of view, that is to say the angle of view which the film records - then it will be identical to the middle (or optimal) pinhole size.

    Ergo ... pinhole size does NOT affect angle of view. Not once the defining boundaries, that is to say the distance from the film plane and the size of the pinhole also include the third variable - the size of the film.

    So a pinhole can be too small in relation to other factors and cause vignetting but larger than optimal will only degrade the quality, but not change the angel of view.

    Details, details!
    To find the answers .... Question them!

  4. #44
    RalphLambrecht's Avatar
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    Pavel

    Did I say pinhole size affects angle of view somewhere?
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  5. #45
    Pavel+'s Avatar
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    Quote Originally Posted by RalphLambrecht View Post
    Pavel

    Did I say pinhole size affects angle of view somewhere?
    No, you said pinhole thickness, not size - and that is what I mean to type in my response - sorry. But it is the same difference. As the light rays move in a straight line the angle of view is determined by the distance and size of the film. Only. In the diagram you show, light will correctly illuminate a wider field in the last example - but it is immaterial as it will miss the film and thus not affect the angle of view.

    Lastly, the thickness has a simple geometric relationship to size - so whether the widest angle is due to size or thickness ... it really does not matter and thus neither does the distinction.

    (None of this is very important - I almost wish I hadn't put in my two cents worth )
    To find the answers .... Question them!

  6. #46
    RalphLambrecht's Avatar
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    Quote Originally Posted by Pavel+ View Post
    ... In the diagram you show, light will correctly illuminate a wider field in the last example - but it is immaterial as it will miss the film and thus not affect the angle of view. ...
    The only point of the diagram is to show that too thick of a pinhole material can cause vignetting. The caption states:

    The pinhole material thickness limits the angle of coverage. Thick materials may reduce the angle of view, and the pinhole will no longer fill the entire negative format.

    Sorry, if I didn't make this sufficiently clear.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  7. #47
    Jim Jones's Avatar
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    Many formulae for optimum pinhole diameters are most valid for on-axis image sharpness. However, both sharpness and illumination dramatically decrease near the edges of ultra wide angle coverage. A somewhat larger than normal pinhole can provide some gain in corner sharpness at the expense of on-axis performance. 30 years ago I improvised a camera to test this. A rough graph of the results is attached. Also, in regard to filters, since the sharpness of pinhole photography is partly dependent on the wavelength of light, there is a very slight gain in sharpness by using blue sensitive film or a blue filter over using a red filter. This, too, has been verified by experimentation, but I don't have the results available.
    Attached Thumbnails Attached Thumbnails OffAxis5.gif  

  8. #48
    RalphLambrecht's Avatar
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    Jim

    Thanks for this graph. It shows extremely valuable data.

    However, before this discussion get too confusing, we must make a difference between resolution and contrast, and concentrate on perceived sharpness. There are two equations for the optimal pinhole diameter: one for max resolution and one for max contrast.

    While a smaller hole will give more resolution (up to a point) a slightly larger hole will provide more contrast and perceived sharpness. The attached MTF shows that and verifies your statement.

    Normally people subconsciously prefer contrast over resolution (high-resolution images are often too soft to be valued as sharp), and therefore, the optimum pinhole diameter based on contrast (and not resolution) is preferred.
    Attached Thumbnails Attached Thumbnails PinholeMTF.jpg  
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

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